The operation of closed hydraulic piston and cylinder assemblies and the problems encountered to compensate for volume displaced by the reciprocation of the piston and piston rod during the operation of the piston and cylinder assembly have been widely known and experienced in the art; and numerous efforts have been made to obviate such noted problems. However, the known efforts to alleviate the noted problems have not always been simple to apply for a particular application, e.g. where it is desirable that air or gas be strictly prohibited from being introduced into the cylinder. One such application is where the incompressibility of the liquid or hydraulic fluid in one of the closed cylinder chambers is used to hold the piston firmly in a given operative position thereof. In any such application, the presence of any air or gas introduced into the cylinder chambers or within the hydraulic fluid would render the use of such piston and cylinder assembly inoperative of any such application.